Recovery of cyanoacetic acid from aqueous inorganic salt solutions



Patented Aug. 30, 1949 RECOVERY OF CYANOACETIC ACID FROM AQUEOUS INORGANIC SALT SOLUTIONS Leonard Nicholl, N yack, and Herbert R. Elkinton,

Blauvelt, N. Y., assignors to Kay-Fries Chemicals, Inc., West liaverstraw, N. Y., a corporation of New York N Drawing. Application June 18, 1947, Serial No. 755,486

4 Claims.

This invention relates to an improved method for recovering anhydrous cyanoacetic acid from aqueous inorganic salt solutions thereof. More particularly, the invention relates to a solvent extraction process wherein a salt-free extract layer is obtained which contains substantially all the cyanoacetic acid under treatment, in solution with some or the water and the extractant, and a second, water-rich layer containing traces of the acid and the solvent with substantially all of the separated salt values, which layer is discarded. The extract layer is then distilled, its water being removed as an azeotrope with the solvent, leaving a distilland comprising a solution of anhydrous cyanoacetic acid and solvent, the components or which can then be separated by distillation.

Cyanoacetic acid is usually produced by the following series of reactions, all being carried out in aqueous solution: 1

The concentration of cyanoacetic acid in the final reaction bath will vary somewhat, depending on the concentrations of the reagents used.

From a. practical and commercial standpoint, it is desirable to have it as high as possible, without resorting to evaporation of water. Whatever the concentrations employed may be, the resulting solution Will be saturated with regard to inorganic salts which are formed at the same time.

Because of these conditions, the recovery of cyanoacetic acid by methods hitherto proposed has been both diihcult and unsatisiactory. The precipitation of the acid as the calcium salt and its recovery by treatment of the calcium salt with sulphuric acid is, a procedure which is both tedious and dlilicult. When the acid is crystallized from aqueous inorganic salt solution, it is found that, due to the very high solubility of the acid in the solution, and also to the tendency of the acid to form a double compound with the inorganic salts present, it is practically impossible to obtain the acid in a state of reasonable purity. Additionally, there is a very controlling factor that the cost of evaporating large amounts of water, which is necessary if this procedure is to be followed, is practically prohibitive. Separation of the acid by distillation is very severely limited by the fact that the acid tends to decompose when the temperature reaches IOU-105 C. As the acid boils around 108" c. at 15 mm. it is prac- 2 tically impossible to separate the acid by distillation from aqueous inorganic salt solutions, without excessive decomposition.

Difierent classes of organic compounds vary widely in their ability to serve as extractants for the recovery of cyanacetic acid from aqueous salt solutions. Non-polar compounds, such as the aliphatic and aromatic hydrocarbons are very poor extractants, as are the halogen derivatives of such hydrocarbons. oxygenated compounds, such as alcohols, ethers, esters, ketones, exhibit varying abilities to act as extractants. Thus it is found that in general as an extractant becomes more polar in character, it tends to be a better extractant for cyanacetic acid.

It has also been noted that within any one homologous series, even if the lower member is a good extractant, this property falls rapidly as the series is ascended. Thus, in the case of the ethers, diethyl ether is a fairly good extractant for cyanacetic acid, whereas dipropyl, di-isopropyl and dibutyl ether are poor extractants, with the dibutyl ether much poorer than di-isopropyl and dipropyl ethers. The self-same phenomenon occurs with cyanacetic esters. Methyl cyanacetate is a good extractant for cyanacetic acid; ethyl cyanacetate is noticeably less so, and propyl and butyl cyanacetates are so much less satiserties for cyanacetic acid as to be frequently impractical to use.

It has also been found that in most cases wherethe compound is a good extractant for cyanacetic acid, i. e., where there is a relatively high concentration of acid in the extract layer at equilibrium, there is also a relatively high concentration of water and inorganic salts. This results from the fact that with the high concentration of acid, the extract layer is now a good solvent for water, since the acid is very soluble in water and has a very high aflinity for it, and the extract layer is also a good solvent for the salts as a result of the presence of. a relatively. high concentration of water.

While it is highly desirable to use as an extractant a chemical compound which will produce a relatively high concentration of acid in the extract layer, it is also important to note that certain limiting factors mustbe present in order to make the use of any extractant commercially feasible or practical. The azeotropic properties of the azeotrope of: the extractant with water should b sueh tli'at'it nossesses'as high a concentration of water as is possible, with the result that the extract layer may be dehydrated as easily.-

removed in the extract canbe separated as'a'r'r azeotrope with the solvent, thus simplifying the recovery of the extractant. The; extractant should be susceptible of ready separation from its solution with the anhydrous cyanacetic acid, and, therefore, should not form a constant'boiling mixture with the acid to be extracted, nor should itboils closetctheacidastomake separation by distillation: difllcul-t. Additionally, the extractants would; have o. be. cheap. in, price. in ord to. e, usa e. practical y. on a ar e. scale. inally the extractant. m st not react with. the material ein extracted,

t wi l, now. be, scenthat n rder to. ch cse a. material which wil ser e. as a at s ctory ex rect nt a ractica com rom se sv neces ary r ards ro erties.- he. present inven ion. s: ex r stan o c an? ticec d would. at be rbneetqshqwthe hi hes coneen ra ion. f. p e. a hecza ra t but r the ha nawh qh will she high co centra i n of acid in the as-ts.as ee iblew th ut, an a he. am ima. a s n samu h w te nd. no ni.' .a t.: ;$el fi 9ni hat-extra. stepsarqneces; am dseparate either, o bat Hemme x ra By, h m rev zn nta of he; nxent ve h rein, such.d eimblere e ts t Q ai ed. a da Wa n al e xt a tis q ined which. ran i rea y. rca di' e di e t m? @Qidexam-wine rane es ew. beeaiwaddha thades rahle esu s, yams-me h l nq ula e za ey anbee urea oba r l i ne... nd; med r, as e..- s e. best l -around; 9 2891 walla. 1e, er. the; ur ose,

h p t sq t ese qemblqunqa a e s p i-r.

Boiling point N. B. degrees L16- Azeotro e with'wa'tr M composition '(H'nOlboiling '"point Solubility mwa r Water-in methyl isobutyl' ketone fr-Tfff t? ticable scale, to maintainithe Watercontent-of.

Em. the. purp es of thereaction mixture at as low a. value..or volume 1 1300.1bs. of water.inaaglassilinedvessel. Thisstep. is endothermic; andisheating may..be, required;

Thereafter, 500lbs.l.o1soda1ash.arei added gradu:

ally, care being taknzto:allow'ior evolutiomof. carbon dioxide: 'WllBhlcthel SOda;-.8Sh-.i-S all re:

4 acted, the sodium cyanide (490 lbs.) is added in the dry state, graduallwfat a temperature of 25 tb-30 C. After: the dryi sodium cyanide has all been added, the temperature is raised to 50 C. for two hours. The equivalent Weight of concentratedsu lphurip acid is then added, gradually, and with coolingfsdthat the temperature is not permitted torise'above 50 C. An appreciable amountofcsaltis precipitated, and this precipitate is separated from the reaction solution by means ofa centrifuge, leaving a reaction solution which l, I. act laye w ths mewa er. a danaa Qll be tom ay r. ummies-miner amqu tsqtke one nd ub tantia ly all. at. the salt..- t. has. e n eund t a t e. onten 19 i. lithe ac dic. he, x r ct yers s. app mdc atsl .-7,- n%@.tQ- 21. 1%, as the concentration of the acid in the aqueous xn ar ea mm was 2.

nary temperatureshas mtg-19ml s in Isobutyl :39. 9 i

Mesityl Oxide Per cent, '18 6 ."3

It isto be noted-that-the water is present in the extract layersin solutionwith the ketones.

with methyl isobutyl k-tone as extracta-ntthe exhausted aqueous salt solution wnrconmm approximately cyanacetic acidand .4 methyl isobutyl keto'ne."

The extract layer istreatedto-reccven; the acid by first distilling oft the water content as anaz'eotro'pe' with the ketone=untilall of the-water is removed." The water-ketone azeotrope balls at- 8'7.9-".G. 'T-he liretone-rich layer canbe reusedi in the process, and the watenrich, brine-layer. may be discarded. I Wham the; dissolved -.1etone. is tobe recovered; a suitable .solvent.l'is used-..to, extract thefsamel The. waterlislremoyedlfrom. the extract -layer aswaneg azeotroper with. the sol-r vent, leavingla residue; comprising; anhydrousl cyanoacetic. acid Y dissolved; insolvent.- The ,re mainderiofthesolventis distilled. ofiaby maintain-h. ing thenwater=freelliquid vundcrs-vacuuml and-at. a. liquidc temperaturesbelowi 9021C ,Y.'I-he;,. dehy,-. drated. extract,- is,.concentrated.1to,.am !wmnattelikv 70% cyanacetic... acid; which has been, round; torequire... a. final pressure oi. app .OX.i iI.1afiely,. 114,- mm.. At thissta esme solution is oded-ta'rwm; tempe aturexzsaqo. atlwmch palata -inflame:- cetic,.acidxrystalliz fis lltm the. solmi n- 11 2: acid is. separated by filtration fro n the mothe l uor, the mtratipnsbei ssq -9141595 ES-R9 with air. Thereafter the filtrate is washed with Jenzene and vacuum dried. The yield of the rystallized acid is approximately 80%. The bal- .nce of the acid remaining in the mother liquor ipproximates 17% 01' the original amount and nay be reused when the next batch is crystallized. the yields calculated for these operations are as ollows:

(1) Yield of acid in extract after concentratng, calculated on the acid originally present in iqueous salt solution. 95%.

(2) Yield of acid in a single crystallization rom the dehydrated concentrated extract 50 to depending on the concentration of the exract. The total recovery of the acid on crystalization is found to be approximately 95%. The iroperties of the acid recovered are as follows:

lcidity 98-100% lolor Light tan color delting point 65-6'7 )dor Very slight ketone odor The acid is also recovered by concentrating the extract to approximately 95% cyanacetic acid :ontent, which step will require a final vacuum if approximately 5 mm. with a liquid temperature |f not over 95-100 C. The concentrated extract 5 then blown with air at 8590 C. and under a aeuum of mm. Proceeding under these conlitions, a product exhibiting the following proper- .ies is obtained:

lcidity 95-96% Zolor Dark brown vielting point 64-65 )dor Very slight ketone odor By way or resume, it is to be noted that the deirable results of the present invention follow as a 'esult of the discovery of the special properties f methyl isobutyl ketone, and in particular the act that the concentration of water in the sol- 'ent extract, at equilibrium, is less than the con- :entration of water-methyl isobutyl ketone azeozrope.

The unexpected efliciencies of the present )rocess resulting from the use of methyl isoutyl ketone and mesityl oxide can best be apireciated by a comparison with another comiound, methyl ethyl ketone, which has been irominently mentioned as a suitable extractant 'or recovery of cyanoacetic acid from aqueous norganic salt solutions. These compounds are :ompared by means of the composition of the exract at equilibrium when extracting solutions of :yanacetic acid in aqueous inorganic salt solution :ontainlng 17% and 24% 01 acid respectively, is is follows:

IATIO OF KEIONEAINODACID NECESSARY TO EXTRACT DEHYDRATE 4. 26 4. 03 2. 48 1. 9G 1. 0o 1. 0o 1. 0o 1. 0o

lzeotrope composition:

Water l1. 0 24. 3 34. 8 Ketone 88. 0 75. 7 65. 2

Considering the methyl ethyl ketone as the prior art standard, it will be noted that the water amounts to approximatel 35.6% of the ketone and water in the extract. Since the ketonewater azeotrope contains only 11% water, additional ketone would have to be added in order to completely dehydrate the extract. This results in the fact that the total minimum ratio of methylethyl ketone to acid, necessary to insure the complete dehydration of the acid, is 4.26 to 1.00.

With mesityl oxide the ratio of ketone to acid is 1.96 to 1.00. When the acid is to be crystallized, even more ketone will be required. Additionally, an appreciable proportion of this extractant is tied. up as a constant boiling mixture with water.. While this constant boiling mixture may be used as an extractant, there will always be an excess over that required for the extraction, which excess will have to be recovered, and the constant boil-- ing mixture will not separate into two layers at ordinary temperature due to the fact that the solubility of water in methyl ethyl ketone is 13.5%, which is greater than the concentration of Water in the azeotrope, which is onl 11%. Therefore, a special added step will be required to recover the methyl ethyl ketone from its con stant boiling mixture. Because of the fact that there is such a. high concentration of water present at equilibrium in the extract, when'using methyl ethyl ketone, there is also an appreciable amount of inorganic salts contained in the solution (6.5% in the case of the 24.6% cyanacetic acid solution). These inorganic salts precipitate out on dehydration. On a large commercial scale this means another operation.

Contrasting the disabilities of the prior art methyl ethyl ketone extractant with the presentl proposed, and highly eificient methyl isobutyl ketone, it will be noted that the situation is appreciably different. The water in the extract, when methyl isobutyl ketone is used, amounts to 6.5% of the ketone and water alone. The ketonewater azeotrope contains 24.3% water. It is obvious from this that the extract can be dehydrated easily, without the necessity of adding more extractant, as has been found necessary in the case of the methyl ethyl ketone. The ratio of methyl isobutyl ketone to acid will be seen to be 4.03 to 1. Thus, in spite of the fact that more methyl isobutyl ketone is required per unit weight of acid than of methyl ethyl ketone, in the extraction, the large amount of methyl ethyl ketone required to dehydrate the extract actually means that somewhat more methyl ethyl ketone (4.26 lbs.) than methyl isobutyl ketone (4.03) per pound of acid extracted is required for the complete operation of extraction and dehydration of the extract. Where methyl isobutyl ketone is used, there is much less water present, under equilibrium conditions, in the extract, and little if any inorganic salt in the solution. Hence no salt precipitates on dehydration of the extract, thereby eliminating another process step or operation.

It will now be appreciated that there has been provided a novel method for the direct recovery of cyanacetic acid from aqueous inorganic salt solutions containing the same, which process involves the use of special extractants of the type of 6 carbon alkyl chains such as methyl isobutyl ketone and its corresponding unsaturated compound mesityl oxide.

What is claimed is:

1. A process for recovering anhydrous cyanoacetic acid from an aqueous inorganic salt solution thereof, which comprises extracting the acid from saidssolution \with a solvent comprisingan alipl'ialtic. ketone'of the: group consisting, of methyl isobutyl ketone and mesityl oxide to forman acid-rich, aqueous ketonelayer, and asubstantially acid and ketone-free, salt-rich, briny layer, separating the layers, distilling. the acid-ketone layerto remove. the water asanrazeotropelwith the ketone and leave an anhydrous acid-ketone solution, and recovering the acid from :said isolation.

2.'-In.a continuous process for the recovery of anhydrouscyanoacetic acid from an aquecuslnorganic salt solution, thereof, the steps which consist in passing such solutioncountercurrentto a stream of an extractantcomprising methyl isobutyl' ketone to form a saltz-free extract: layer comprising a solution of cyanoacetic acid, water, and methyl isobutyl ketone, and a water-rich layer containing substantially allthe salt:with

traces of cyanoacetic acid and methyl isobutyl;

ketone, concentrating the salt-free extract layer by distilling off the Water as an azeotropezwith themethyl-lsobutyl ketone to completely remove all of the water present in the extractand vthereafter crystallizing the cyanoacetic acid from the residual-'water-free solvent solution.

3-. In a continuous process for the recovery-of 'anhydrouscyanoacetic acid from an aqueous inorganic salt solution containing-1745 percent acid, the steps which consistin passing suchsolution countercurrent-to a streamof an *extractant comprising methyl isobutyl ketone to form a substantially salt-free extract layer' comprising a solution of cyanoacetic acid; water, and methyl isobutyl ketone, and a water-rich layercontaining substantially all the salt with traces of-;-cya-noacetic acid and methyl isobutyl ketone; discardin the said water-rich salt layer,- and concentratin the salt-free extract layer by distilling off th water as an azeotrope with methyl isobutylketon to completely remove all of the water present ii the extract and thereafter crystallizing substan tially, anhydrous cyanoacetic acidfrom the water free solvent solution.

4. In a continuous process for therecovery o anhydrous cyanoacetic acid from an aqueousin organic salt solution'thereof containing17-259 of the acid, the steps which consist in passing, sucl solution countercurrent to a .jstream of w an ex tractant comprising mesityl oxide to form a sub stantially salt-free extract layer comprising solutionof cyanoacetic acid, water, andmesit; oxide, and a water-rich layer containing substan tially all the salt with traces of cyanoacetic aci and mesityl oxide, concentrating the V salt-ire acid extract layer by distilling off-the water asai azeotrope with mesityl oxide to completely'lremov all of the water present in the extract and there after crystallizing substantiallyanhydrous cyano acetic acid from .the water-freesolvent solutior LEONARD NICHOL Q, HERBERT; R. ELKIN'ITON.

REFERENCES CITED The following references are of record :in-th file of this patent:

UNITED v STATES PATENTS Number Name Date 2,150,154 Cope Mar. 14, 193 2,338,834 Britton et a1. Jan. 11, 194 

